Probes have become widely used in the oil, gas and process industries to measure and monitor phenomena such as internal corrosion in the system. Examples of this are the ER or LPR probes or weight-loss couplons which are screwed into process pipes, well-heads, or water injection systems etc. By using a short threaded nipple (access fitting) with an internal thread and a sealing system, a probe can be screwed into a pipe so that it is in direct contact with the process medium.
The different types of probes and weight-loss coupons must be changed frequently. This is because of the variation and short lifetime of the probes and the planned inspection of the weight-loss coupons.
For many years, such replacement operations have been done by the help of mechanical tools or retriever equipment. The prior art operation consists of a ball valve which is screwed directly onto the access nipples in which the probe is mounted. An internal, axially moveable and rotatable bar is screwed onto a mechanical retriever, which consists of a double cylinder. The retriever is then mounted on the ball valve. The bar engages the threaded plugs and or probes to be screwed in or out of the nipple. The probe can be moved from the double, sealed cylinder through the open ball valve into the nipple in the alternative the probe can be moved from the nipple into the sealed cylinder. Once the probe has been moved through the ball valve into the retriever cylinder, the valve can be closed. The retriever cylinder can then be removed from the valve and the probe removed from the cylinder. It is then possible to attach a new probe onto the guide bar in the retriever cylinder, screw the retriever with the probe onto the valve, then open the ball valve, and guide the probe into position on the nipple again as it passes through the ball valve. Once the probe is completely screwed in the retriever and ball valve can be unscrewed. A considerable disadvantage with this traditional prior art mechanical system is the extreme length of the cylinder with the bar, typically 1.8-2.0 meters. This imposes considerable restrictions on use of the system. The jack of space means that it is difficult to service nipples which are close to other pipes, near the wall/floor or roof etc. The moveable cylinder unit with its bar also represents a danger in that sudden, axial movements of the bar caused by a lack of pressure-compensation in the retriever could injure the operator. A further difficulty is the considerable weight of such units. This means that the transport of the unit around a plant and its operation are both strenuous tasks.